Method and Apparatus for secondary base station change in mobile wireless communication system

ABSTRACT

A method and apparatus for secondary base station change in a mobile communication system with multiple are provided. Method for secondary node change includes transmitting to a target SN a control message requesting conditional secondary node change, receiving from the target SN a Xn message including conditional secondary node change information, transmitting to a terminal LTE DL message for conditional secondary node change, receiving from the terminal a 1st LTE UL message including a transaction identifier, receiving from the terminal a conditional reconfiguration identifier and transmitting to a source SN a control message for data forwarding.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2021-0103238, filed on Aug. 5, 2021, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a mobile communication system withconditional secondary base station change. More specifically, thepresent disclosure relates to a secondary node change method and anapparatus for use in the mobile communication system with conditionalreconfiguration configuration managed by a master node.

To meet the increasing demand for wireless data traffic since thecommercialization of 4th generation (4G) communication systems, the 5thgeneration (5G) system is being developed. For the sake of high, 5Gsystem introduced millimeter wave (mmW) frequency bands (e. g. 60 GHzbands). In order to increase the propagation distance by mitigatingpropagation loss in the 5G communication system, various techniques areintroduced such as beamforming, massive multiple—input multiple output(MIMO), full dimensional MIMO (FD-MIMO), array antenna, analogbeamforming, and large-scale antenna. In addition, base station isdivided into a central unit and plurality of distribute units for betterscalability. To facilitate introduction of various services, 5Gcommunication system targets supporting higher data rate and smallerlatency.

SUMMARY

Aspects of the present disclosure are to address the problems ofconditional secondary node change. Accordingly, an aspect of the presentdisclosure is to provide a method and an apparatus for providing theconfiguration information for conditional secondary node change.

In accordance with an aspect of the present disclosure, a method of abase station in mobile communication system is provided. In the method,the base station transmits to a target node a base station controlmessage for SGNB addition request, the base station receives from thetarget node a base station control message for SGNB addition response,the base station transmits LTE RRC message to UE for conditionalsecondary node change, the base station receives a first RRC responsemessage, the base station receives a second RRC response message, thebase station performs SGNB release procedure with source node for SNSTATUS TRANSFER and data forwarding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the architecture of an LTE system andan E-UTRAN to which the disclosure may be applied;

FIG. 2 is a diagram illustrating a wireless protocol architecture in anLTE system to which the disclosure may be applied;

FIG. 3 is a diagram illustrating the architecture of an 5G system and aNG-RAN to which the disclosure may be applied;

FIG. 4 is a diagram illustrating a wireless protocol architecture in an5G system to which the disclosure may be applied;

FIG. 5 is a diagram illustrating the architecture of an EN-DC to whichthe disclosure may be applied;

FIG. 6A is a diagram illustrating EN-DC operation performed by a UE anda base station according to the first embodiment of the presentdisclosure;

FIG. 6B is a diagram illustrating another EN-DC operation performed by aUE and a base station according to the first embodiment of the presentdisclosure;

FIG. 7 is a diagram illustrating a structure of LTE reconfigurationmessage for the 1^(st) reconfiguration procedure;

FIG. 8 is a flow diagram illustrating an operation of a master basestation according to the first embodiment of the present disclosure;

FIG. 9 is a flow diagram illustrating an operation of a terminalaccording to the first embodiment of the present disclosure;

FIG. 10 is a block diagram illustrating the internal structure of a UEto which the disclosure is applied;

FIG. 11 is a block diagram illustrating the configuration of a basestation according to the disclosure;

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms used, in the following description, for indicating accessnodes, network entities, messages, interfaces between network entities,and diverse identity information is provided for convenience ofexplanation. Accordingly, the terms used in the following descriptionare not limited to specific meanings but may be replaced by other termsequivalent in technical meanings.

In the following descriptions, the terms and definitions given in the3GPP standards are used for convenience of explanation. However, thepresent disclosure is not limited by use of these terms and definitionsand other arbitrary terms and definitions may be employed instead.

In the following descriptions, UE and terminal are used as sameterminology.

Table 1 lists the acronyms used throughout the present disclosure.

TABLE 1 Acronym Full name 5GC 5G Core Network 5GS 5G System 5QI 5G QoSIdentifier ACK Acknowledgement AMF Access and Mobility ManagementFunction ARQ Automatic Repeat Request AS Access Stratum ASN.1 AbstractSyntax Notation One BSR Buffer Status Report BWP Bandwidth Part CACarrier Aggregation CAG Closed Access Group CAG-ID Closed Access GroupIdentifier CG Cell Group CHO Conditional Handover CIF Carrier IndicatorField CORESET Control Resource Set CPC Conditional PSCell Change CQIChannel Quality Indicator C-RNTI Cell RNTI CSI Channel State InformationDC Dual Connectivity DCI Downlink Control Information DRB (user) DataRadio Bearer DRX Discontinuous Reception ECGI E-UTRAN Cell GlobalIdentifier eNB E-UTRAN NodeB EN-DC E-UTRA-NR Dual Connectivity EPCEvolved Packet Core EPS Evolved Packet System E-RAB E-UTRAN Radio AccessBearer ETWS Earthquake and Tsunami Warning System E-UTRA EvolvedUniversal Terrestrial Radio Access E-UTRAN Evolved Universal TerrestrialRadio Access Network FDD Frequency Division Duplex FDM FrequencyDivision Multiplexing GBR Guaranteed Bit Rate HARQ Hybrid AutomaticRepeat Request HPLMN Home Public Land Mobile Network IDC In-DeviceCoexistence IE Information element IMSI International Mobile SubscriberIdentity KPAS Korean Public Alert System L1 Layer 1 L2 Layer 2 L3 Layer3 LCG Logical Channel Group MAC Medium Access Control MBR Maximum BitRate MCG Master Cell Group MCS Modulation and Coding Scheme MeNB MastereNB MIB Master Information Block MIMO Multiple Input Multiple Output MMEMobility Management Entity MN Master Node MR-DC Multi-Radio DualConnectivity NAS Non-Access Stratum NCGI NR Cell Global Identifier NE-DCNR-E-UTRA Dual Connectivity NGEN-DC NG-RAN E-UTRA-NR Dual ConnectivityNG-RAN NG Radio Access Network NR NR Radio Access NR-DC NR-NR DualConnectivity PBR Prioritised Bit Rate PCC Primary Component CarrierPCell Primary Cell PCI Physical Cell Identifier PDCCH Physical DownlinkControl Channel PDCP Packet Data Convergence Protocol PDSCH PhysicalDownlink Shared Channel PDU Protocol Data Unit PLMN Public Land MobileNetwork PRACH Physical Random Access Channel PRB Physical Resource BlockPSCell Primary SCG Cell PSS Primary Synchronisation Signal PUCCHPhysical Uplink Control Channel PUSCH Physical Uplink Shared Channel PWSPublic Warning System QFI QoS Flow ID QoE Quality of Experience QoSQuality of Service RACH Random Access Channel RAN Radio Access NetworkRA-RNTI Random Access RNTI RAT Radio Access Technology RB Radio BearerRLC Radio Link Control RNA RAN-based Notification Area RNAU RAN-basedNotification Area Update RNTI Radio Network Temporary Identifier RRCRadio Resource Control RRM Radio Resource Management RSRP ReferenceSignal Received Power RSRQ Reference Signal Received Quality RSSIReceived Signal Strength Indicator SCC Secondary Component Carrier SCellSecondary Cell SCG Secondary Cell Group SCS Subcarrier Spacing SDAPService Data Adaptation Protocol SDU Service Data Unit SeNB SecondaryeNB SFN System Frame Number S-GW Serving Gateway SI System InformationSIB System Information Block (S-/T-) SN (Source/Target) Secondary NodeSpCell Special Cell SRB Signalling Radio Bearer SRS Sounding ReferenceSignal SSB SS/PBCH block SSS Secondary Synchronisation Signal SULSupplementary Uplink TDD Time Division Duplex TDM Time DivisionMultiplexing TRP Transmit/Receive Point UCI Uplink Control InformationUE User Equipment UL-SCH Uplink Shared Channel UPF User Plane Function

Table 2 lists the terminologies and their definition used throughout thepresent disclosure.

TABLE 2 Terminology Definition Cell combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources. Global cell An identity to uniquely identifying anNR cell. It is consisted of identity cellIdentity and plmn-Identity ofthe first PLMN-Identity in plmn- IdentityList in SIB1. gNB nodeproviding NR user plane and control plane protocol terminations towardsthe UE, and connected via the NG interface to the 5GC. Information Astructural element containing single or multiple fields is referred aselement information element. NR NR radio access PCell SpCell of a mastercell group. Primary SCG For dual connectivity operation, the SCG cell inwhich the UE Cell performs random access when performing theReconfiguration with Sync procedure. Serving Cell For a UE inRRC_CONNECTED not configured with CA/DC there is only one serving cellcomprising of the primary cell. For a UE in RRC_CONNECTED configuredwith CA/DC the term ‘serving cells’ is used to denote the set of cellscomprising of the Special Cell(s) and all secondary cells. SpCellprimary cell of a master or secondary cell group. Cell Group in dualconnectivity, a group of serving cells associated with either the MeNBor the SeNB. En-gNB node providing NR user plane and control planeprotocol terminations towards the UE, and acting as Secondary Node inEN-DC. Master Cell in MR-DC, a group of serving cells associated withthe Master Node, Group comprising of the SpCell (PCell) and optionallyone or more SCells. Master node in MR-DC, the radio access node thatprovides the control plane connection to the core network. It may be aMaster eNB (in EN-DC), a Master ng-eNB (in NGEN-DC) or a Master gNB (inNR-DC and NE- DC). NG-RAN either a gNB or an ng-eNB. node PSCell SpCellof a secondary cell group. Secondary For a UE configured with CA, a cellproviding additional radio Cell resources on top of Special Cell.Secondary in MR-DC, a group of serving cells associated with theSecondary Cell Group Node, comprising of the SpCell (PSCell) andoptionally one or more SCells. Secondary in MR-DC, the radio accessnode, with no control plane connection to node the core network,providing additional resources to the UE. It may be an en-gNB (inEN-DC), a Secondary ng-eNB (in NE-DC) or a Secondary gNB (in NR-DC andNGEN-DC). Conditional a PSCell change procedure that is executed onlywhen PSCell PSCell execution condition(s) are met. Change gNB Central alogical node hosting RRC, SDAP and PDCP protocols of the gNB or Unit(gNB- RRC and PDCP protocols of the en-gNB that controls the operationof CU) one or more gNB-DUs. The gNB-CU terminates the F1 interfaceconnected with the gNB-DU. gNB a logical node hosting RLC, MAC and PHYlayers of the gNB or en- Distributed gNB, and its operation is partlycontrolled by gNB-CU. One gNB-DU Unit (gNB- supports one or multiplecells. One cell is supported by only one gNB- DU) DU. The gNB-DUterminates the F1 interface connected with the gNB-CU. E-RAB An E-RABuniquely identifies the concatenation of an S1 Bearer and thecorresponding Data Radio Bearer. When an E-RAB exists, there is aone-to-one mapping between this E-RAB and an EPS bearer of the NonAccess Stratum (NAS) as defined in TS 23.401 [3].

Table 3 lists abbreviations of various messages, information elementsand terminologies used throughout the present disclosure.

TABLE 3 Abbreviation Message/IE/Terminology LTE RECNFRRCConnectionReconfiguration LTE RECNF CMPRRCConnectionReconfigurationComplete CAPENQ UECapabilityEnquiry CAPINFUECapabilityInformation NR RECNF RRCReconfiguration NR RECNF CMPRRCReconfigurationComplete ULIT ULInformationTransferMRDC SGNB ADD REQSGNB ADDITION REQUEST SGNB ADD REQ ACK SGNB ADDITION REQUEST ACKNOWLEDGESGNB REL REQ SGNB RELEASE REQUEST SGNB REL REQ ACK SGNB RELEASE REQUESTACKNOWLEDGE SGNB RECNF CMP SGNB RECONFIGURATION COMPLETE Transaction IDrrc-TransactionIdentifier TCSPCELL Target Candidate SpCell CRIDCondReconfigurationId

Table 4 explains technical terminologies used throughout the presentdisclosure.

TABLE 4 Terminology Definition PSCell change It means the current PSCellchanges to a new PSCell. It includes intra-SN PSCell change and inter-SNPSCell change. PSCell addition is also considered as PSCell change.CG-ConfigInfo IE The IE is transferred from MN to SN or from CU to DU.It includes following information ue-CapabilityInfo includes variousinformation for UE capability MeasResultList2NR includes measurementresults on the candidate cells for serving cell DRX configuration of MCGCG-Config IE The IE is transferred from SN to MN or from CU to DU. Itincludes following information NR RRCReconfiguration which includes SCGconfiguration informatino. MN transfer the NR RRCReconfiguration messageto UE without modifying it Information related to SCG bearer. Itincludes the information indicating the security key for the bearer DRXconfiguration of SCG ARFCN indicating the center frequency of PSCellmeasConfig It is configuration related to measurement and set by MN andSN separately. It comprises at least one measurement object(measObject), at least one report configuration (ReportConfig) and atleast one measurement identity (measId). A measObject is identified by aMeasObjectId. A reportConfig is identified by a ReportConfigId. A measIdcomprises a measObjectId and a reportConfigId. MeasId instructs UE toperform a specific operation when measurement result on the associatedmeasObject fulfils condition set by ReportConfigId TCSPCELL It indicatestarget candidate SPCell. In the 1^(st) procedure, plurality of cells ofa single target node can be configured as target candidate SpCell.TCSPCELL can be a cell selected, by MN or S-SN, among the cells forwhich UE report measurement result. Throughout the 1^(st) procedure, oneof plurality of TCSPCELL becomes PSCell

FIG. 1 is a diagram illustrating the architecture of an LTE system andan E-UTRAN to which the disclosure may be applied.

The E-UTRAN consists of eNBs (102, 103, 104), providing the E-UTRA userplane (PDCP/RLC/MAC/PHY) and control plane (RRC) towards the UE. TheeNBs (102, 103, 104) are interconnected with each other by means of theX2 interface. The eNBs are also connected to the MME (MobilityManagement Entity) (105) and to the Serving Gateway (S-GW) (106) bymeans of the S1. The S1 interface supports a many-to-many relationbetween MMEs/Serving Gateways and eNBs. MME (105) and S-GW (106) may berealized either as a physical node or as separate physical nodes.

The eNB (102, 103, 104) hosts the functions listed below.

Functions for Radio Resource Management such as Radio Bearer Control,Radio Admission Control, Connection Mobility Control, Dynamic allocationof resources to UEs in uplink, downlink and sidelink(scheduling); and

IP and Ethernet header compression, uplink data decompression andencryption of user data stream; and

Selection of an MME at UE attachment when no routing to an MME can bedetermined from the information provided by the UE; and

Routing of User Plane data towards Serving Gateway; and

Scheduling and transmission of paging messages (originated from theMME).

The MME (105) hosts the functions such as NAS signaling, NAS signalingsecurity, AS security control, S-GW selection, Authentication, Supportfor PWS message transmission and positioning management.

The S-GW (106) hosts the functions such as packet routing andforwarding, transport level packet marking in the uplink and thedownlink, mobility anchoring for inter-eNB handover etc.

FIG. 2 is a diagram illustrating a wireless protocol architecture in anLTE system to which the disclosure may be applied.

User plane protocol stack consists of PDCP (201 or 202), RLC (203 or204), MAC (205 or 206) and PHY (207 or 208). Control plane protocolstack consists of NAS (209 or 210), RRC (211 or 212), PDCP, RLC, MAC andPHY.

Each protocol sublayer performs functions related to the operationslisted in the table 5.

TABLE 5 Sublayer Functions NAS authentication, mobility management,security control etc RRC System Information, Paging, Establishment,maintenance and release of an RRC connection, Security functions,Establishment, configuration, maintenance and release of SignallingRadio Bearers (SRBs) and Data Radio Bearers (DRBs), Mobility, QoSmanagement, Detection of and recovery from radio link failure, NASmessage transfer etc. PDCP Transfer of data, Header compression anddecompression, Ciphering and deciphering, Integrity protection andintegrity verification, Duplication, Reordering and in-order delivery,Out-of-order delivery etc. RLC Transfer of upper layer PDUs, ErrorCorrection through ARQ, Re- segmentation of RLC data PDUs,Concatenation/Segmentation/Reassembly of SDU, RLC re-establishment etc.MAC Mapping between logical channels and transport channels,Multiplexing/demultiplexing of MAC SDUs belonging to one or differentlogical channels into/from transport blocks (TB) delivered to/from thephysical layer on transport channels, Scheduling information reporting,Priority handling between UEs, Priority handling between logicalchannels of one UE etc. PHY Channel coding, Physical-layer hybrid-ARQprocessing, Rate matching, Scrambling, Modulation, Layer mapping,Downlink Control Information, Uplink Control Information etc.

FIG. 3 is a diagram illustrating the architecture of an 5G system and aNG-RAN to which the disclosure may be applied.

5G system consists of NG-RAN (301) and 5GC (302). An NG-RAN node iseither:

-   -   a gNB, providing NR user plane and control plane protocol        terminations towards the UE; or    -   an ng-eNB, providing E-UTRA user plane and control plane        protocol terminations towards the UE.

The gNBs (305 or 306) and ng-eNBs (303 or 304) are interconnected witheach other by means of the Xn interface. The gNBs and ng-eNBs are alsoconnected by means of the NG interfaces to the 5GC, more specifically tothe AMF (Access and Mobility Management Function) and to the UPF (UserPlane Function). AMF (307) and UPF (308) may be realized as a physicalnode or as separate physical nodes.

A gNB (305 or 306) or an ng-eNBs (303 or 304) hosts the functions listedbelow.

Functions for Radio Resource Management such as Radio Bearer Control,Radio Admission Control, Connection Mobility Control, Dynamic allocationof resources to UEs in uplink, downlink and sidelink(scheduling); and

IP and Ethernet header compression, uplink data decompression andencryption of user data stream; and

Selection of an AMF at UE attachment when no routing to an MME can bedetermined from the information provided by the UE; and

Routing of User Plane data towards UPF; and

Scheduling and transmission of paging messages; and

Scheduling and transmission of broadcast information (originated fromthe AMF or O&M); and

Measurement and measurement reporting configuration for mobility andscheduling; and

Session Management; and

QoS Flow management and mapping to data radio bearers; and

Support of UEs in RRC_INACTIVE state; and

Radio access network sharing; and

Tight interworking between NR and E-UTRA; and

Support of Network Slicing.

The AMF (307) hosts the functions such as NAS signaling, NAS signalingsecurity, AS security control, SMF selection, Authentication, Mobilitymanagement and positioning management.

The UPF (308) hosts the functions such as packet routing and forwarding,transport level packet marking in the uplink, QoS handling and thedownlink, mobility anchoring for mobility etc.

FIG. 4 is a diagram illustrating a wireless protocol architecture in an5G system to which the disclosure may be applied. User plane protocolstack consists of SDAP (401 or 402), PDCP (403 or 404), RLC (405 or406), MAC (407 or 408) and PHY (409 or 410). Control plane protocolstack consists of NAS (411 or 412), RRC (413 or 414), PDCP, RLC, MAC andPHY.

Each protocol sublayer performs functions related to the operationslisted in the table 6.

TABLE 6 Sublayer Functions NAS authentication, mobility management,security control etc RRC System Information, Paging, Establishment,maintenance and release of an RRC connection, Security functions,Establishment, configuration, maintenance and release of SignallingRadio Bearers (SRBs) and Data Radio Bearers (DRBs), Mobility, QoSmanagement, Detection of and recovery from radio link failure, NASmessage transfer etc. SDAP Mapping between a QoS flow and a data radiobearer, Marking QoS flow ID (QFI) in both DL and UL packets. PDCPTransfer of data, Header compression and decompression, Ciphering anddeciphering, Integrity protection and integrity verification,Duplication, Reordering and in-order delivery, Out-of-order deliveryetc. RLC Transfer of upper layer PDUs, Error Correction through ARQ,Segmentation and re-segmentation of RLC SDUs, Reassembly of SDU, RLCre-establishment etc. MAC Mapping between logical channels and transportchannels, Multiplexing/demultiplexing of MAC SDUs belonging to one ordifferent logical channels into/from transport blocks (TB) deliveredto/from the physical layer on transport channels, Scheduling informationreporting, Priority handling between UEs, Priority handling betweenlogical channels of one UE etc. PHY Channel coding, Physical-layerhybrid-ARQ processing, Rate matching, Scrambling, Modulation, Layermapping, Downlink Control Information, Uplink Control Information etc.

FIG. 5 is a diagram illustrating the architecture of an EN-DC to whichthe disclosure may be applied.

E-UTRAN supports MR-DC via E-UTRA-NR Dual Connectivity (EN-DC), in whicha UE is connected to one eNB (501 or 502) that acts as a MN and oneen-gNB (503 or 504) that acts as a SN. The eNB (501 or 502) is connectedto the EPC (505) via the S1 interface and to the en-gNB (503 or 504) viathe X2 interface. The en-gNB (503 or 504) might also be connected to theEPC (505) via the S1-U interface and other en-gNBs via the X2-Uinterface.

LTE and NR are expected to coexist for considerable time to come. Asingle operator could deploy both LTE and NR within its network. Forsuch case, providing to a UE both stable connection with LTE and highdata rate with NR is possible if UE is connected to both. EN-DC enablessimultaneous data transfer via LTE and NR.

In EN-DC, frequent SN change could happen due to narrow coverage of NR.SN change requires PSCell. change, so they are technically synonymous.PSCell change procedure in general is consisted with that MN or S-SN getaware that PSCell change is needed, that T-SN determines theconfiguration of the new PSCell and that MN informs LIE theconfiguration of the new PSCell. Depending on a given circumstances,either immediately changing the PSCell upon receiving the PSCellconfiguration information or changing PSCell when certain condition ismet could be appropriate. In the disclosure, the latter is 1^(st)reconfiguration (delayed reconfiguration or conditional reconfiguration)and the former is 2^(nd) reconfiguration. (or immediate reconfigurationor normal reconfiguration.).

The disclosure provides operations of the terminal and the base stationfor the 1^(st) reconfiguration and for the 2^(nd) reconfiguration.

FIG. 6A is a diagram illustrating EN-DC operation performed by a UE anda base station according to the first embodiment of the presentdisclosure. FIG. 6B is a diagram illustrating another EN-DC operationperformed by a UE and a base station according to the first embodimentof the present disclosure.

In 610, MN (602) decides SN change based on measurement result reportedby UE (601).

MN (602) transmits, to T-SN (604), SGNB ADD REQ requesting resourceallocation for the UE's EN-DC operation. SGNB ADDREQ includes followinginformation.

-   -   1^(st) information: Information indicating whether SGNB addition        procedure is for 1^(st) reconfiguration or for 2^(nd)        reconfiguration.    -   2^(nd) information: It is included If 1^(st) reconfiguration is        requested. 1^(st) reconfiguration execution condition and        related information determined by MN. It includes execution        condition and execution condition cell group IE.    -   Measurement results on T-SN's cells    -   Data radio bearer configuration related information: Information        on DRBs to be established. It can be used for T-SN's call        admission control.    -   Maximum data rate related information: Expected maximum data        rate of the call. It can be used for T-SN's call admission        control.

The 1^(st) information can be realized by various embodiments.

1^(st) reconfiguration and 2^(nd) reconfiguration can be distinguishedby introducing new code point in SGNB Addition Trigger Indication IE. Inthe current specifications, SGNB Addition Trigger Indication IE isdefined to indicate one of SN change, inter-eNB HO and intra-eNB HO. Inthis disclosure, new code point called Conditional PSCell Change isadditionally defined for SGNB Addition Trigger Indication IE. If the IEindicates one of SN change, inter-eNB HO and intra-eNB HO, it is for the2^(nd) reconfiguration procedure. If the IE indicates Conditional PSCellChange, it is for the 1^(st) reconfiguration procedure.

Alternatively, Conditional PSCell Change (CPC) IE can be introduced toindicate the 1^(st) reconfiguration procedure. CPC IE can indicatewhether the corresponding procedure is to replace the currentconditional reconfiguration or to initiate new conditionalreconfiguration. Or a list of cells determined based on measurementresults from UE, for example list of TCSPCELLs, can be used as the1^(st) information.

In 615, T-SN (604) performs call admission control and decides whetherto accept the request or not. If decide to accept, T-SN (604) sends, toMN (602), SGNB ADD REQ ACK.

The message includes information on the resource allocated to the UE,for example IE related to maximum data rate, IE related to radio bearer,logical identity to identify UE on X2 interface and Cell groupconfiguration (CG-Config) IE. The message also includes a 3^(rd)information indicating whether the procedure is 1^(st) reconfigurationprocedure or 2^(nd) reconfiguration procedure. The 3^(rd) informationcan be a specific cell's global identity and maximum number ofConditional PSCell Change/Addition preparations for a UE toward a targetGNB.

MN (602) determines whether to perform 1^(st) reconfiguration procedureor 2^(nd) reconfiguration procedure. If MN transmitted 1^(st)information and 2^(nd) information and received 3^(rd) information, MNperforms 1^(st) reconfiguration procedure. If MN did not transmit 1^(st)information and 2^(nd) information and did not receive 3^(rd)information, MN performs 2^(nd) reconfiguration procedure. If MN decidesto perform 1^(st) reconfiguration procedure, MN proceed to 620. If MNdetermines to perform 2^(nd) reconfiguration procedure, MN proceeds to670. Alternatively, if SGNB ADD REQ includes conditional reconfigurationrequest information and SGNB ADD ACK includes conditionalreconfiguration response information, MN consider 1^(st) reconfigurationprocedure is accepted and perform 1^(st) reconfiguration procedure. IfSGNB ADD REQ does not include conditional reconfiguration requestinformation or SGNB ADD ACK does not include conditional reconfigurationresponse information, MN consider 2^(nd) reconfiguration procedure isaccepted and perform 2^(nd) reconfiguration procedure.

In 620, MN (602) transmits to UE (601) 1^(st) LTE RECNF.

The structure of LTE RECNF to configure 1^(st) reconfiguration for EN-DCUE is explained in FIG. 7 .

In 625, UE transmits to MN 1^(st) LTE RECNF CMP comprising 1^(st)Transaction id.

Optionally, UE determines execution condition based on executioncondition IE and execution condition cell group IE. The executioncondition IE comprises one or two MeasID(s). The execution conditioncell group IE is information indicating either master cell group (or MN)or secondary cell group (or SN). Alternatively, the informationindicates only master cell group and absence of the information can beinterpreted as secondary cell group being indicated. MeasID in theexecution condition IE is the MeasID of the MeasConfig of the cell groupindicated by execution condition cell group IE. UE considers the MeasIDof the indicated cell group's MeasConfig as the execution condition. UErecognize which measurement object to measure, and which conditiontriggers the 1^(st) reconfiguration execution based on the variousparameters of MeasObject associated with the MeasID and based on thevarious parameters of ReportConfig associated with the MeasID.

The execution condition is determined by MN or S-SN. MN or S-SN expressthe determined execution condition using a MeasID defined in itsMeasConfig. UE needs to know which node between MN and SN sets theexecution condition to recognize what the MeasID really means. In thedisclosure, above information is indicated to the UE via executioncondition cell group IE.

In LTE, MeasID indicating a value between 1 and 32 and MeasID-v1250indicating a value between 33 and 64 are defined. In the disclosure,former is 5 bit measld and latter is 5 bit measld-ext. In NR, MeasIDindicating a value between 1 and 64 is defined. In the disclosure, it is6 bit measld.

MN can inform T-SN measld for execution condition via SGNB ADD REQ. MNcan transform a 5bit measld or a 5bit measld-ext to 6bit measld andinclude it in SGNB ADD REQ. If MN selects a 1^(st) 5bit measld forexecution condition, MN sets the MSB of 6 bit measld to 0 and setsremaining of 6bit measld to the 1^(st) 5 bit measld. If MN selects a2^(nd) 5 bit measld for execution condition, MN sets the MSB of 6bitmeasld to 1 and sets remaining of 6 bit measld to the 2^(nd) 5bitmeasld.

UE receives 6 bit measld for the execution condition via RECNF. If theexecution condition is determined by S-SN, UE determines the executioncondition without transforming 6 bit measld. If the execution conditionis determined by MN, UE determines the execution condition bytransforming 6 bit measld either to 1^(st) 5 bit measld or to 2^(nd) 5bit measld.

In 630, UE performs conditional reconfiguration evaluation to determinewhether condition for conditional reconfiguration is fulfilled. UEdetermines whether measurement result for a cell corresponding to thecell identity indicated in 3^(rd) NR RECNF (i.e. TCSPCELL) fulfillsexecution condition. If so, UE executes conditional reconfiguration byapplying 2^(nd) NR RECNF of the cell fulfilling the execution condition.

In 635, UE performs random access procedure with T-SN. During randomaccess procedure, UE transmits preamble to a base station, the basestation transmits random access response to the UE, UE performs PUSCH(Physical Uplink Shared Channel) transmission toward the base stationand the base station transmits contention resolution message to UE.

In 640, UE transmits ULIT to MN. ULIT includes 1^(st) NR RECNF CMP.1^(st) NR RECNF CMP includes 3^(rd) Transaction id. If MN receives ULITfrom UE with ongoing 1^(st) reconfiguration procedure, MN recognizesthat the 1^(st) reconfiguration is executed and performs requiredactions. For example, MN forwards to T-SN 1^(st) NR RECNF CMP includedin ULIT and initiates SGNB release procedure with S-SN.

In 645, MN transmits SGNB RECNF CMP to T-SN. The message includes 1^(st)NR RECNF CMP. SN recognize the 1^(st) NR RECNF CMP is the response to2^(nd) NR RECNF from that 1^(st) NR RECNF CMP includes 3^(rd)Transaction id.

In 650, MN (602) transmits SGNB REL REQ to S-SN (603) so that requiredsteps such as SN STATUS TRANSFER procedure can be taken place. SGNB RELREQ includes GTP tunnel information for data forwarding.

In 655, S-SN (603) receives SGNB REL REQ and starts a specific timer andtransmits SGNB REL REQ ACK to T-SN (604). S-SN (603) releases theresource allocated to the UE and discard related information upon expiryof the timer.

In 660, S-SN (603) transmits to MN (602) SN STATUS TRANSFER includinguplink/downlink PDCP SN and HFN. MN forward it to T-SN (604). SN STATUSTRANSFER includes HFN and PDCP SN.

T-SN (604) determines, based on SN STATUS TRANSFER, HFN and PDCP SN ofdownlink PDCP packet to be transmitted to UE and PDCP SN of uplink PDCPpackets for which retransmission is to be requested.

In 665, S-SN (603) forwards PDCP packets to MN. MN forwards them to T-SN(604). T-SN (604) transmits those downlink PDCP packets to UE. S-SN canperform data forwarding based on PDCP COUNT of the first PDCP PDU fordata forwarding.

If 2^(nd) reconfiguration procedure is to be performed, MN proceeds to670 after receiving SGNB ADD ACK.

In 670, MN(602) transmits to S-SN(603) SGNB REL REQ so that S-SN(603)can initiate necessary subsequent procedures. SGNB REL REQ includes GTPtunnel information for data forwarding.

In 671, S-SN (603) receives SGNB REL REQ and starts a specific timer andtransmits SGNB REL REQ ACK to T-SN (604). S-SN (603) releases theresource allocated to the UE and discard related information upon expiryof the timer.

In 675, MN (602) transmits to UE(601) 2^(nd) LTE RECNF. The 2^(nd) LTEreconfiguration includes 5^(th) Transaction id and 4^(th) NR RECNF whichincludes 6^(th) Transaction id and PSCell configuration information.T-SN(604) generates 2^(nd) NR RECNF, include it in CG-Config IE anddeliver it to MN via SGNB ADD ACK. MN(602) includes 2^(nd) NR RECNF in2^(nd) LTE RECNF and transmit it to UE(601).

In 676, UE (601) receives 2^(nd) LTE RECNF and transmits to MN (602)2^(nd) LTE RECNF CMP which includes 5^(th) Transaction id and 2^(nd) NRRECNF CMP. 2^(nd) NR RECNF CMP includes 6^(th) Transaction id. MNrecognizes based on the 5^(th) Transaction id that the 2^(nd) LTE RECNFCMP is response to 2^(nd) LTE RECNF.

In 677, MN(602) include, in SGNB RECNF, CMP 2^(nd) NR RECNF CMP includedin 3^(rd) LTE RECNF CMP and transmit it to T-SN(604). T-SN recognizes,based on 6th Transaction id, 2^(nd) NR RECNF CMP is response to 4^(th)NR RECNF. Consequently, 2^(nd) LTE RECNF CMP includes at least twoTransaction id. One of them is used by MN and the other is forwarded toT-SN by MN and used by T-SN.

After transmitting SGNB REL REQ ACK, S-SN(603) in 685 transmits toMN(602) SN STATUS TRANSFER and MN transmits it to T-SN(604).

In 690, S-SN(603) forwards to MN downlink PDCP packets and MN forwardsthem to T-SN(604). T-SN(604) transmits the PDCP packets to UE.

In 678, after transmitting 3^(rd) LTE RECNF CMP, UE(601) performs PSCellchange procedure towards the PSCell indicated in 2^(nd) NR RECNF at 678.

In 680, UE performs random access in the PSCell. After completion ofrandom access, UE(601) consider PSCell change procedure is completed andresume data transfer with T-SN(604).

As disclosed above, in the 1^(st) procedure MN initiates SGNB RELEASEprocedure after UNIT or 2^(nd) uplink LTE control message is receivedfrom UE. On the other hands in the 2^(nd) procedure, MN initiates SGNBRELEASE procedure before ULIT or 2^(nd) uplink LTE control message isreceived from UE. The reason for MN to behave differently depending onthe procedure is to control such that S-SN(603) can perform operationrelated to data forwarding at appropriate point of time.

FIG. 7 is a diagram illustrating a structure of LTE reconfigurationmessage for the 1^(st) reconfiguration procedure

LTE RECNF includes 1^(st) Transaction id generated by MN and 1^(st) NRRECNF (702) generated by T-SN. 1^(st) NR RECNF includes variousinformation depending on the purpose of the related procedure. For the1^(st) reconfiguration, 1^(st) NR RECNF includesconditionalReconfiguration (710) which includes at least oneCondReconfigToAddMod IE (703 or 720 or 721).

Each CondReconfigToAddMod IE includes conditional ReconfigurationIdentity (or 2^(nd) NR control information identity) (704), executioncondition (705), execution condition cell group (722) and 2^(nd) NRRECNF (706) carrying various configuration information. 2^(nd) NRcontrol information identity is mandatorily present. Executioncondition, 2^(nd) NR RECNF and execution condition cell group areoptionally present. If the 2^(nd) NR control information identityincluded in the 2^(nd) NR control information is new identity, executioncondition and 2^(nd) NR RECNF are mandatorily present and executioncondition cell group is optionally present.

The 2^(nd) NR RECNF includes radio bearer configuration (708), counterfor security key (709) and 3^(rd) NR RECNF (707). The 3^(rd) NR RECNFincludes secondaryCellGroup IE which includes configuration informationof TCSPCELL.

Therefore, a single 1^(st) NR RECNF for 1^(st) reconfiguration procedureincludes plurality of TCSPCELL configuration information. Each ofplurality of TCSPCELL configuration information is associated with asingle execution condition IE and a single execution condition cellgroup IE.

The 1^(st) NR RECNF includes 2^(nd) Transaction ID, the 2^(nd) NR RECNFincludes 3^(rd) Transaction ID and the 3^(rd) NR RECNF includes 4^(th)Transaction ID,

FIG. 8 is a flow diagram illustrating an operation of a master nodeaccording to the first embodiment of the present disclosure.

In 801, 1^(st) base station transmits to 3^(rd) base station (T-SN)1^(st) control message related to SGNB addition. The 1^(st) controlmessage can include 1^(st) information and 2^(nd) information.

In 806, 1^(st) base station receives from 3^(rd) base station 2^(nd)control message related to SGNB addition. The 2^(nd) control message caninclude a 3^(rd) information and PSCell configuration information (ortarget SpCell configuration information).

In 811, the 1^(st) base station checks whether 1^(st) condition isfulfilled. The 1^(st) base station proceeds to 816 if 1^(st) conditionis fulfilled. The 1^(st) base station proceeds to 841 if 1^(st)condition is not fulfilled. If the 1^(st) base station has transmittedto 3^(rd) base station 1^(st) control information which include 1^(st)information and has received 2^(nd) control information, from the 3^(rd)base station in response to the 1^(st) control message, 1^(st) conditionis fulfilled.

In 816, 1^(st) base station transmits to UE 1^(st) LTE RECNF whichincludes at least 1^(st) Transaction id and 1^(st) NR RECNF. 1^(st)Transaction id is determined and inserted by 1^(st) base station. 1^(st)NR RECNF is generated by 3^(rd) base station and transmitted to 1^(st)base station. 1^(st) NR RECNF includes at least one 2^(nd) Transactionid and CondReconfigMod IE.

In 821, 1^(st) base station receives, from UE, 1^(st) LTE RECNF CMPwhich includes 1^(st) Transaction id.

1^(st) base station checks if, from UE, ExecutionReport is receivedbefore ULIT is received. If ExecutionReport is received before ULIT,1^(st) base station proceed to 831. If ULIT is received beforeExecutionReport, 1^(st) base station proceeds to 851.

In 826, 1^(st) base station receives from UE ULIT which includes 1^(st)NR RECNF CMP and CRID. 1^(st) NR RECNF CMP includes at least 3^(rd)Transaction id. 1^(st) base station transmits to 3^(rd) base stationSGNB RECNF CMP, which includes at least 1^(st) NR RECNF CMP.

In 831, 1^(st) base station and 2^(nd) base station performs SGNBrelease procedure. In the procedure, 1^(st) base station transmits to2^(nd) base station SGNB REL REQ, 2^(nd) base station transmits to1^(st) base station SGNB REL REQ ACK.

In 836, 1^(st) base station and 2^(nd) base station exchanges SN STATUSTRANSFER and performs data forwarding.

In 861, 1^(st) base station, UE and 2^(nd) base station complete theprocedure and performs EN-DC operation.

In 841, 1^(st) base station and 2^(nd) base station performs SGNBrelease procedure.

In 846, 1^(st) base station transmits to UE 2^(nd) LTE RECNF whichincludes 5^(th)

Transaction id and 4^(th) NR RECNF. 5^(th) Transaction id is determinedand inserted by 1^(st) base station. 4^(th) NR RECNF is generated by3^(rd) base station and transmitted to 1^(st) base station. 4^(th) NRRECNF includes at least 6^(th) Transaction id and PSCell configurationinformation.

In 851, 1^(st) base station receives from UE 3^(rd) LTE RECNF CMP whichincludes 5^(th) Transaction id and 4^(th) NR RECNF CMP. 4^(th) NR RECNFCMP includes at least 6th Transaction id. 1^(st) base station transmitsto 3^(rd) base station SGNB RECNF CMP which includes 3^(rd) NR RECNFCMP.

In 856, 1^(st) base station and 2^(nd) base station exchange SN STATUSTRANSFER and perform data forwarding.

In 861, 1^(st) base station, UE and 2^(nd) base station complete theprocedure and performs EN-DC operation.

FIG. 9 is a flow diagram illustrating an operation of a terminalaccording to the first embodiment of the present disclosure.

In 901, UE reports, to 1^(st) base station (MN or MeNB), UE capabilityrelated to EN-DC and 1^(st) reconfiguration procedure.

-   -   1^(st) capability information: a list of band combinations        supporting EN-DN    -   2^(nd) capability information: a list of band combinations        supporting 1^(st) reconfiguration and EN-DC or list of EN-DC        band combinations supporting 1^(st) reconfiguration    -   3^(rd) capability information: a list of band combinations        comprising two NR bands

2^(nd) capability information indicates NR band of which bandcombination, included in the 1^(st) capability information, supports1^(st) reconfiguration procedure. 2^(nd) capability informationindicates intra-band 1^(st) reconfiguration support.

3^(rd) capability information is list of band combinations with two NRbands and each band combination indicates inter-band 1^(st)reconfiguration is supported between the NR bands. For example, if (N1,N2) is included in 3^(rd) capability information, inter-band 1^(st)reconfiguration between N1 and N2 is supported. NR bands included in theband combinations of 3^(rd) capability information are the NR bandssupporting EN-DC.

A base station to which UE reports its capability, a base station fromwhich UE receives LTE RECNF and a base station with which UE performsrandom access can be different base stations. The reason is because thecapability reported by UE is stored in the core network and capabilityreporting is performed in the initial registration and not performedafterward.

In 906, UE receives LTE RECNF. The LTE RECNF includes 1^(st) NR RECNF.The 1^(st) NR RECNF includes 1^(st) information if the 1^(st) NR RECNFis for 1^(st) reconfiguration. The 1^(st) information includes at leastone 2^(nd) information. In the 2^(nd) information, a 3^(rd) informationand a 4^(th) information are mandatorily present, and a 5^(th)information is optionally present. Information from the 1^(st)information to the 5^(th) information are those defined between UE andbase station. They are different from the 1^(st) information to the3^(rd) information defined between MN and T-SN.

A 2^(nd) information corresponds to a TCSPCELL. A 3^(rd) informationcomprising one or two MeasID defines the execution condition for theTCSPCELL. A 4^(th) information is the 2^(nd) NR RECNF which includesradio bearer configuration, security key information and 3^(rd) NR RECNFfor the configuration information of TCSPCELL. 5^(th) informationindicates for which between MCG and SCG (or between MeNB and SgNB orbetween MN and S-SN) the execution condition is related to.

Each 3^(rd) information and each 5^(th) information define the executioncondition for each associated TCSPCELL (or associated 2^(nd)information). Alternatively, it is also possible to define a common3^(rd) information and a common 5^(th) information applicable to allTCSPCELL (or all 2^(nd) information) included in the 1^(st) NR RECNF. Itis possible to define he common 3^(rd) information and the common 5^(th)information as sub-IE of 1^(st) information. Then UE ignores individual3^(rd) information included under 2^(nd) information. UE applies common3^(rd) information, if present, to all TCSPCELLs included in 1^(st)information. Otherwise, UE applies the 3^(rd) information included foreach TCSPCELL.

A single LTE RECNF includes a single 1^(st) NR RECNF. A single 1^(st) NRRECNF includes plurality of 2^(nd) NR RECNFs. A single 2^(nd) NR RECNFincludes a single 3^(rd) NR RECNF. Therefore, a single LTE RECNFincludes a plurality of 3^(rd) NR RECNFs, a plurality of 3^(rd)information, a plurality of 4^(th) information and a plurality of 5^(th)information. The number of 3^(rd) NR RECNFs, the number of 3^(rd)information and the number of 4^(th) information are same while thenumber of 5^(th) information may be different.

A single RECNF includes a single Transaction id. The LTE RECNF includes1^(st) Transaction id. The 1^(st) NR RECNF includes 2^(nd) Transactionid. The 2^(nd) NR RECNF includes 3^(rd) Transaction id. The 3^(rd) NRRECNF includes 4^(th) Transaction id.

In 911, UE transmits LTE RECNF CMP to the 1^(st) base station. The LTERECFN CMP includes 1^(st) Transaction id.

In 916, UE initiates 1^(st) reconfiguration if 1^(st) reconfigurationinformation is included in 1^(st) NR RECNF in 1^(st) LTE RECNF receivedby UE

In 921, UE determines, based on 3^(rd) information and 5^(th)information, to which cell group (or which node) MeasID indicated in the3^(rd) information is related. If 5^(th) information is absent, UEdetermines that execution condition for the corresponding TCSPCELL isset by S-SN and that the MeasID is related to source SCG (or S-SN). UEinterprets MeasID according to MeasConfig of source SCG (or S-SN). If5^(th) information is present, UE determines that execution conditionfor the corresponding TCSPCELL is set by MN and that the MeasID isrelated to MCG (or MN). UE interprets MeasID according to MeasConfig ofMCG (or MN). Alternatively, if 5^(th) information is present, UEdetermines that execution condition for the corresponding TCSPCELL isset by a CG (or by a node) between MCG and SCG (or between MN and S-SN)and UE interprets MeasID according to the MeasConfig of determined CG(or determined node).

In LTE, MeasID indicating a value between 1 and 32 and MeasID-v1250indicating a value between 33 and 64 are defined. In the disclosure,former is 5 bit measld and latter is 5 bit measld-ext. In NR, MeasIDindicating a value between 1 and 64 is defined. In the disclosure, it is6 bit measld.

MN can inform T-SN measId for execution condition via SGNB ADD REQ. MNcan transform a 5 bit measId or a 5 bit measId-ext to 6 bit measId andinclude it in SGNB ADD REQ. If MN selects a 5 bit measId for executioncondition, MN sets the MSB of 6 bit measId to 0 and sets remaining of 6bit measId to the 5 bit measId. If MN selects a 5 bit measId-Ext forexecution condition, MN sets the MSB of 6 bit measId to 1 and setsremaining of 6 bit measId to the 5 bit measId-Ext.

UE receives 6 bit measId for execution condition in RECNF. If theexecution condition is determined by S-SN, UE determines the executioncondition with 6 bit measId as it is. If the execution condition isdetermined by MN, UE determines the execution condition with 5 bitmeasId or 5 bit measId-Ext transformed from 6 bit measId. If MSB of 6bit measId is 0, UE takes the remaining 5 bit aslst 5 bit measId andselects associated ReportConfig and MeasObject accordingly. If MSB of 6bit measId is 1, UE takes the remaining 5 bit as 5 bit measId-Ext andselects associated ReportConfig and MeasObject accordingly.

In 926, UE performs conditional reconfiguration evaluation. For each2^(nd) information included in 1^(st) information, UE considers theserving cell indicated in 3^(rd) NR RECNF of 2^(nd) information (i.e.target candidate cell) as applicable cell. UE consider the targetcandidate cell as a triggered cell if event associated with the triggercondition for the cell is fulfilled.

In 931, UE executes conditional reconfiguration. UE apply the 2^(nd) NRRECNF for the triggered cell.

In 936, UE transmits to 2^(nd) base station ULIT. ULIT includes 1^(st)NR RECNF CMP. 1^(st) NR RECNF CMP includes 3^(rd) Transaction id. ULITalso includes CRID corresponding to triggered cell (or 2^(nd) NR RECFNcorresponding to triggered cell)

FIG. 10 is a block diagram illustrating the internal structure of a UEto which the disclosure is applied.

Referring to the diagram, the UE includes a controller (1001), a storageunit (1002), a transceiver (1003), a main processor (1004) and I/O unit(1005).

The controller (1001) controls the overall operations of the UE in termsof mobile communication. For example, the controller (1001)receives/transmits signals through the transceiver (1003). In addition,the controller (1001) records and reads data in the storage unit (1002).To this end, the controller (1001) includes at least one processor. Forexample, the controller (1001) may include a communication processor(CP) that performs control for communication and an applicationprocessor (AP) that controls the upper layer, such as an applicationprogram. The controller controls storage unit and transceiver such thatUE operations illustrated in FIG. 9 is performed.

The storage unit (1002) stores data for operation of the UE, such as abasic program, an application program, and configuration information.The storage unit (1002) provides stored data at a request of thecontroller (1001).

The transceiver (1003) consists of a RF processor, a baseband processorand plurality of antennas. The RF processor performs functions fortransmitting/receiving signals through a wireless channel, such assignal band conversion, amplification, and the like. Specifically, theRF processor up—converts a baseband signal provided from the basebandprocessor into an RF band signal, transmits the same through an antenna,and down—converts an RF band signal received through the antenna into abaseband signal. The RF processor may include a transmission filter, areception filter, an amplifier, a mixer, an oscillator, adigital—to—analog converter (DAC), an analog—to—digital converter (ADC),and the like. The RF processor may perform MIMO and may receive multiplelayers when performing the MIMO operation. The baseband processorperforms a function of conversion between a baseband signal and a bitstring according to the physical layer specification of the system. Forexample, during data transmission, the baseband processor encodes andmodulates a transmission bit string, thereby generating complex symbols.In addition, during data reception, the baseband processor demodulatesand decodes a baseband signal provided from the RF processor, therebyrestoring a reception bit string.

The main processor (1004) controls the overall operations other thanmobile operation. The main processor (1004) process user input receivedfrom I/O unit (1005), stores data in the storage unit (1002), controlsthe controller (1001) for required mobile communication operations andforward user data to I/O unit (1005).

I/O unit (1005) consists of equipment for inputting user data and foroutputting user data such as a microphone and a screen. I/O unit (1005)performs inputting and outputting user data based on the mainprocessor's instruction.

FIG. 11 is a block diagram illustrating the configuration of a basestation according to the disclosure.

As illustrated in the diagram, the base station includes a controller(1101), a storage unit (1102), a transceiver (1103) and a backhaulinterface unit (1104).

The controller (1101) controls the overall operations of the main basestation. For example, the controller (1101) receives/transmits signalsthrough the transceiver (1103), or through the backhaul interface unit(1104). In addition, the controller (1101) records and reads data in thestorage unit (1102). To this end, the controller (1101) may include atleast one processor. The controller controls transceiver, storage unitand backhaul interface such that base station operation illustrated inFIG.8 are performed.

The storage unit (1102) stores data for operation of the main basestation, such as a basic program, an application program, andconfiguration information. Particularly, the storage unit (1102) maystore information regarding a bearer allocated to an accessed UE, ameasurement result reported from the accessed UE, and the like. Inaddition, the storage unit (1102) may store information serving as acriterion to deter mine whether to provide the UE with multi—connectionor to discontinue the same. In addition, the storage unit (1102)provides stored data at a request of the controller (1101).

The transceiver (1103) consists of a RF processor, a baseband processorand plurality of antennas. The RF processor performs functions fortransmitting/receiving signals through a wireless channel, such assignal band conversion, amplification, and the like. Specifically, theRF processor up—converts a baseband signal provided from the basebandprocessor into an RF band signal, transmits the same through an antenna,and down—converts an RF band signal received through the antenna into abaseband signal. The RF processor may include a transmission filter, areception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC,and the like. The RF processor may perform a down link MIMO operation bytransmitting at least one layer. The baseband processor performs afunction of conversion between a baseband signal and a bit stringaccording to the physical layer specification of the first radio accesstechnology. For example, during data transmission, the basebandprocessor encodes and modulates a transmission bit string, therebygenerating complex symbols. In addition, during data reception, thebaseband processor demodulates and decodes a baseband signal providedfrom the RF processor, thereby restoring a reception bit string.

The backhaul interface unit (1104) provides an interface forcommunicating with other nodes inside the network. The backhaulinterface unit (1104) converts a bit string transmitted from the basestation to another node, for example, another base station or a corenetwork, into a physical signal, and converts a physical signal receivedfrom the other node into a bit string.

1. A method by a Master Node (MN), the method comprising: transmittingto a target Secondary Node (SN) a first base station control message,the first base station control message includes a list of target SpecialCell (SpCell); transmitting to a terminal a first Downlink (DL) message,the first DL message includes a first identifier and one or moreCondReconfigToAddMod, each of the one or more CondReconfigToAddModincludes an execution condition and a second identifier and areconfiguration message; receiving from the terminal a first Uplink (UL)message, the first UL message includes the first identifier; receivingfrom the terminal a second UL message, the second UL message includesthe second identifier, the second identifier corresponds to thereconfiguration message in the CondReconfigToAddMod; and transmitting toa source SN a second base station control message.
 2. The method ofclaim 1, wherein the second base station control message is a messagerequesting release of the source SN
 3. (canceled)
 4. (canceled)
 5. AMaster Node (MN) in a wireless communication system, the MN comprising:a transceiver configured to transmit and receive a signal; and acontroller configured to control the transceiver to: transmit to atarget Secondary Node (SN) a first base station control message, thefirst base station control message includes a list of target SpecialCell (SpCell); transmit to a terminal a first Downlink (DL) DL message,the first DL message includes a first identifier and one or moreCondReconfigToAddMod, each of the one or more CondReconfigToAddModincludes an execution condition and a second identifier and areconfiguration message; receive from the terminal a first Uplink (UL)message, the first UL message includes the first identifier, the firstidentifier corresponds to the first DL message; receive from theterminal a second UL message, the second UL message includes the secondidentifier, the second identifier corresponds to the reconfigurationmessage in the CondReconfigToAddMod; and transmit to a source SN asecond base station control message.